<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
	<title></title>
</head>
<body>
   选择您的爱好：
	  <input type="checkbox" name="box" id="box1" value="跳水" />跳水
	  <input type="checkbox" name="box" id="box2" value="跑步" />跑步
	  <input type="checkbox" name="box" id="box3" value="听音乐" />听音乐
	  <input type="button" name="button" id="button" onclick="checkbox()" value="提交" />
</body>
<script type="text/javascript">
	function checkbox(){
		var str=document.getElementsByName("box");
		var chestr="";
		for (var i=0;i<str.length;i++){
		  if(str[i].checked == true){
		   chestr+=str[i].value+",";
		  }
		}
		if(chestr == ""){
		  alert("请先选择一个爱好～！");
		}
		else{
		  alert("您先择的是："+chestr);
		}
	}
</script>
</html>